Topic 8. The cell membrane – structure and functions. Glycocalyx (cell coat).
Covers the plasma membrane's phospholipid bilayer, with its hydrophilic heads and hydrophobic tails, and the integral, peripheral and transmembrane proteins it carries. It then sets out the membrane's functions and composition, including cholesterol's effect on fluidity, before turning to the glycocalyx, its carbohydrate makeup and roles. The note also describes trilaminar appearance under TEM, freeze-fracture findings, and staining methods such as PAS, Sudan black and lectin labelling.
Topic 8 of 59 in the MU Pleven syllabus for Cytology (Medicine, Year 1). The free AceMed note covers it in 5 sections, about 709 words (5 min of reading), with 14 flashcards.
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TOPIC 8. The cell membrane – structure and functions. Glycocalyx (cell coat).
Plasma membrane
Functions of plasma membrane:
Composition:
Glycocalyx
Plasma membrane
The membrane enclosing a cell is made up of two phospholipids layers making up a phospholipid bilayer. This membrane has two different parts to it –
a hydrophilic phosphate head and
hydrophobic lipid tail – amphipathic
The phospholipids are arranged so that the tails face each other on the inside and the heads face towards the outside of the membrane.
There are pores or channels in the cell's plasmamembrane which are made up of certain proteins that control the movement of water and nutrients in and out of the cell.
Proteins make up a large part of the membrane. There are integral proteins, transmembrane or peripheral proteins. Integral proteins are incorporated directly within the lipid bilayer, whereas peripheral proteins are bound to one of the membrane surfaces. Transmembrane proteins often form channels.
Membrane proteins which are components of large enzyme complexes are usually less mobile, especially those involved in the transduction of signals. Such protein complexes are located in specialised membrane patches called lipid rafts with higher concentrations of cholesterol and saturated fatty acids.
Cholesterol makes the bilayer more fluid but decreases permeability of water soluble molecules.
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